The present invention relates to snowboards and related recreational devices. In particular, it relates to an improved construction of such a device to reduce the overall level of vibration or chatter and enhance its control, thereby substantially enhancing the performance of the device as well as its safety of use. In certain aspects the invention applies to related devices such as toboggans, water skis and runnerless sleds, and to a family of wide ski-like recreational articles, such as telemark or stunt skis.
A snowboard as commonly understood is a relatively flat, elongated sliding platform upon which a user rides upright, in the manner of a ski, sliding and turning for recreational purposes. Generally, snowboards are used on downhill ski slopes, and the board itself has the general size and shape of a water ski, about 1.25 by 0.25 meters, approximately halfway between the dimensions and shapes of a downhill ski, and a sled or toboggan. A snowboard differs from a pair of skis in several important respects. Namely, it has a single elongated sliding surface, rather than a pair of surfaces, and it is controlled by the action of shifting weight with both boots bearing on the single board rather than separately steering or allocating weight between two narrow skis. Furthermore, a snowboard is generally constructed so that its bending stiffness is less than that of a ski. This softness allows the board to be controlled fairly easily by feel, rather than requiring skilled technical training, since it allows slight shifts in weight to effect noticeable differences in the ground-engaging surface that effects steering and braking.
In practice, one boot of the wearer is generally in a mount positioned nearer to the front of the board, and the second boot is mounted somewhat behind the first, allowing the user to shift his weight distribution between the two positions and lean one way or another on the central weight-bearing region. By shifting weight between feet and altering the direction of bearing of the load, the user effects varying amounts of drag or frictional sliding against the bottom surface, and also changes the engagement of edges with the snow, allowing the board to be steered much like a water ski as if it were riding against a fluid surface, and also like a downhill ski that bites at its edges to control the direction of motion. While precise speed and steering control characteristics vary depending on the nature of the underlying snow and the terrain upon which the board is traveling, and are highly individual or intuitive in the ensemble, in general by evenly distributing the weight the board is made to glide faster while by leaning to make the direction of bearing off-vertical or by redistributing weight, the board may be made to steer to one side or the other, or to effect a braking drag and reduce its velocity.
The foregoing principles of operation apply equally well to basic or rudimentary embodiments of a snowboard, such as the dining hall trays often used by children in lieu of sleds, and to the more advanced consumer products often made of advanced materials and having special characteristics of surface friction, shape, stiffness and strength. Indeed, the more advanced consumer products are engineered to attain quite high speeds and achieve reasonable steering and control at these velocities. However, mechanically speaking, a snowboard is a plate, a two-dimensional sheet of material. As such, running in contact with the ground""s surface, it is subject to a number of induced vibrations or resonances. Because their construction is relatively flexible, these states may result in significant chatter at higher speeds as driving forces are exerted on the plate. While in general objectionable oscillations of the snowboard can be limited by simply traveling at low to moderate speeds along gentle surface conditions, a snowboard is more fun and physically challenging to use at higher speeds in exotic or more rugged terrains. Under highly stressed conditions, the driving forces may quickly introduce chatter which impairs steering and may render even simple sliding motion less efficient. Indeed, with snowboards it is not uncommon for a user to generate a great deal of noise and vibration even while traveling at a relatively low speed. As the user progresses to higher speeds and other control maneuvers, structural vibration of the snowboard may introduce instabilities, or inefficiencies or defects of control.
Thus, it would be desirable to provide a snowboard in which structural vibration is better controlled.
It would also be desirable to provide such a snowboard in which desirable characteristics of stiffness, weight and size are maintained while improving overall damping.
These and other desirable ends are obtained in a snowboard having a generally elongated sheet body extending over a two-dimensional region and defining a sliding surface. A central portion of the sheet body supports the user, and the body extends forwardly, rearwardly and laterally outward of the central portion to its bounding edge. Strain elements are positioned adjacent the top surface near the edge to capture strain energy distributed in an anterolateral portion of the board. The strain elements transduce this energy to electrical energy, which is shunted so as to damp the structure. In one embodiment, the strain elements are distributed in sheets having a surface area of about 10-200 cm2 and a thickness under approximately two, and preferably under one millimeter. Preferably, the strain elements are shunted by a resistive shunt, or a combination of a resistive shunt with one or more other elements such as inductive or capacitive elements, calculated to define a resonant circuit for the electrical charge at a target frequency. The target frequency in turn may be a frequency which is measured, or which is computed from the geometric dimensions and stiffness or other physical characteristics of the snowboard, to be a plate resonance of the board. In a practical example for one model of snowboard, the shunt is tuned to a resonance band about 60 Hz and controls a torsion-like oscillation of high amplitude that affects engagement of the steering edge of the board.